1. Field of the Invention
The present invention relates to a housing for temperature measuring apparatus and in particular to a housing for a pyrometer used for measuring the temperature of components in hostile environments.
2. Description of Related Art
It is known to use pyrometers to measure the temperature of rotors in gas turbine engines. The temperature of the blades of the rotor can be measured by mounting the pyrometers through apertures in the engine casing. The pyrometers consist of a lens which focuses radiation emitted from the blade of the rotor onto a radiation sensor. The radiation is focused either directly onto the radiation sensor or via a radiation guide such as a fibre optic cable. The pyrometers experience high temperatures when mounted on the engine casing and contaminants such as soot or other combustion products from the engine are deposited onto the external surface of the lens. These contaminants build up reducing the amount of radiation transmitted to the sensor. The pyrometers are also susceptible to spurious measurements caused by stray radiation being reflected from the engine casing.
Pyrometers working in such hostile environments are provided with housings which permit a flow of fluid over the external surface of the pyrometers to keep it cool. A cooling fluid, such as air, passes over the external surface of the pyrometer after which it is ducted externally of the housing and vented safely away. A proportion of the cooling fluid is however ducted over the external surface of the lens to purge it and reduce the amount of contaminants that are deposited onto the lens. The flow of purging air over the lens exhausts into the vicinity of the test target such as the rotating blades of a gas turbine. The purge air adversely affects the test environment and should the purge air impact the blades an accurate measurement of their temperature is difficult to achieve.